A smart card, also known as an IC-card or a chip card, is a flat normally plastic card that may be as large as a credit card or, in particularly when used as an SIM (subscriber identity module), as small as a postage stamp. Such a card carries active and passive circuit elements. When used, for instance, as a SIM card it has a small processor and enough memory to hold data regarding the identity and preferences of a user. Such a SIM card is commonly used in a cellular telephone to allow a user to transfer his or her phone book and other data from one phone to another.
The card reader must fulfill several functions in addition to the obvious one of forming connections between contact points on the card and traces of the printed-circuit board normally carrying th holder. First of all it must hold and protect the card physically, something that is particularly important as, for instance, in a cell phone the card holder is in the bottom of the battery compartment where it is exposed as batteries are changed. In addition the card holder must shield the card, in particular from inductive and RF (radio-frequency) fields, another problem particularly present in a cell phone where the card is located a few centimeters from a transmitter.
Thus the typical card holder as described in U.S. Pat. No. 5,226,826 has a cover provided with flanges forming a slot into which the card can be slid. The cover is pivotal on a plastic base between an open position in which the slot is exposed for insertion and removal of the card and a closed position flush with the base. Spring contacts in the base bear against terminals on the card in the closed position, and in turn are connected to SMD (surface-mount device) contacts that themselves are soldered to a circuit board or similar support in the device equipped with the card holder.
For best shielding, the standard practice is to make the cover of electrically conductive material, normally metal, and to ground it. The holder can have contacts in the base that engage the cover as in U.S. Pat. No. 5,718,609. Such systems have the disadvantage that the ground connection is not sure. Such use of ground contacts in the base engaging the cover means that another SMD connection must be made between the ground contacts in the base and the support, normally a circuit board, to which the base is fixed, and this extra connection is also capable of failure.